In order to establish and maintain reliable and high quality two-way communication services via satellite and in order to avoid interference to an existing service caused by unauthorized and/or out-of-tolerance transmission, operators of earth station terminals are requested to perform a pre-transmission alignment (line-up) when accessing a satellite for the first time.
For this purpose, the initial line-up phase focuses on the effective isotropic radiated power EIRP, on frequency and antenna alignment, in order to ensure correct and interference free access to the satellite.
Thus, the antenna of an earth station terminal must both be pointed correctly at the antenna of the respective satellite and, in the case of linear polarization, it must also be oriented about its axis to maximize reception of the linearly polarized signal.
For this purpose, an antenna for linear polarized signals must be set up with particular care. In particular, if the setup is defective, the antenna transmits both with the required polarization and with the perpendicular polarization, which causes interference to other services. Consequently, standards generally require an earth station transmitting with linear polarization to satisfy a minimum polarization discrimination requirement.
In order to meet these requirements, one of the problems of installing low cost small earth station terminals is that for the initial antenna alignment and terminal configuration a service technician is required which needs to be trained to install bi-directional satellite communication systems. Consequently the deployment of a telecommunication system in which a geostationary satellite communicates with a plurality of ground stations consumes a lot of time and money (traveling costs, expenses, etc.).
Therefore it is an object of the invention, to simplify the line-up process in order to enable local distributors or even clients to get the satellite terminal operational by themselves (self install).
According to the invention, this object is realized with a method for the alignment of an earth station antenna with a satellite antenna, wherein a reference signal, emitted by the earth station antenna is analyzed in a monitoring station and the reference signal is used as a carrier for authentication information about the earth station terminal.
The present invention provides a simple solution for the need to send information about the earth station terminal. In praxis, a so called CW signal (Continuous Wave signal), that is to say, a sinus signal is used as reference signal. According to the invention, the information is modulated on this signal by on-off keying the CW signal. Mathematically this is a form of digital modulation of the signal. Because the on-off keying is done with a very slow bitrate (eg 2 bits/sec.), so the bandwidth of the modulated signal is very low. In order to underline, that very-low-rate modulation happens, the expression on-off keying will be used in the following preferably.
In order to increase the information rate the CW signal may be modulated with different levels of amplitude instead of applying pure on-off keying.
Preferred embodiments of the invention are described in the dependent claims.
The object of the invention is also realized with a System comprising:                an earth station terminal with an antenna and with means for generating the modulated reference signal        a Monitoring Station with means for the detection and identification of line-up requests and means for monitoring the co-polar and cross-polar components of the signal transmitted from the earth station.        